Receiver gain control circuit



y; 3 B. D. H. TELLEGEN ET AL 88,178

RECEIVER GAIN CONTROL CIRCUIT Filed April 19, 1954 m i m 1 INVENTORS BA-WAMRDUS 0.19. TELLEGEA/ JOf/A/VA/ES A../. BOUMA/V f/E/PRE 52 4 BY 7). Wm ATTORNEY Patented July 27, 1937 UNH'E'E d'lAhS PATENT QFFEQ RECEIVER GAIN CONTROL CIRCUIT Application April 19, 1934, Serial No. 721,368 In the Netherlands May 18, 1933 Claims.

This invention relates to a circuit arrangement for volume control of amplifiers, in which the slope of the tube is regulated by means of the grid bias.

It may occur in this case that it is desired that the volume to be supp-lied by the amplifier is influenced by two magnitudes which are entirely independent of each other. This is the case, for instance, when in order to achieve a uniform amplification over a large range of frequencies the slope of the tube is made to decrease in accordance with the tuning of the amplifier to high frequencies, and when using at the same time automatic volume control, with which the slope is regulated in inverse sense with the strength of the incoming signal.

The first purpose is attained, for instance, by having the tuning condenser actuate a potentiometer contact which is connected to the grids of the, high frequency tubes. This permits to impress a high negative bias on the grids of the tubes when tuning to high frequencies, and a small one when tuning to low frequencies. Automatic volume control can be achieved in a known manner by having the bias of the grids acted upon by the drop of potential caused in a resistance by the direct current component of the detected oscillations.

According to the present invention the grid bias of the amplifying tubes is simultaneously influenced by two magnitudes so that the slope of the tubes, and accordingly also the volume supplied by the amplifier, vary in accordance with both magnitudes.

The novel features which we believe to be characteristic of our invention are set forth in particularity in the appendedclaims. The invention itself, however, both as to its organization and method of operation, will best be understood by reference tothe following description, taken in connection with the drawing, in which we have indicated diagrammatically several circuit organizations whereby our invention may be carried into effect.

45 In the drawing:-

Figs. 1, 2- and 3 show different embodiments of the invention.

Fig. 1 represents an arrangement in which the grid bias of high frequency amplifiers is influenced on one hand by voltage variations depending on the amplitude of the received carrier wave, and on the other hand by voltages whose value is rendered dependent on the frequency of the oscillations to be amplified. The arrangement shown in the drawing comprises only the elements which are required for a good understanding of the part of the amplifying arrangement to which the invention relates.

The conductors l and 2 are connected to a source of direct current energy and earthe'd at the point A. Between these conductors is provided the potentiometer R1 to which is connected a second potentiometer leading from the point a to earth across the resistances R2 and R3. The point of connection of the resistances R2 and R3 is connected to the anode of the rectifyingdiode' 3, which thus obtains a small positive bias (the reason thereof will be set out hereinafter). Of course, the rectifying diode can be replaced by any other rectifier adapted for this purpose, for instance, also by a rectifying-amplifyingtube.

The rectified low frequency oscillations will traverse the resistance R3 and are applied through the regulating contact c to the grid of a low frequency amplifying tube (or to the grid of a rectifying-amplifying-tube). By means of the contact c the volume to be supplied can be controlled by hand.

The drop of potential in the resistance R3 which depends on the strength of the incoming signals, is used for regulating automatically the negative grid voltage of the high frequency amplifying tubes. 7

The conductor 2 includes a resistance R5. The voltage drop occurring therein sets up a negative potential with respect to earth at the end of the conductor 2. Over the resistance R5 can slide a contact d which is mechanically coupled, for instance, with the driving arrangement of the tuning condensers of the tunable grid circuits of the high frequency tubes. In this manner the drop of potential along the resistance R5 can be used for decreasing the slope of the high frequency tubes if the tubes are tuned to the reception of high frequencies.

Consequently, the negative grid voltage of the high frequency tubes must simultaneously be rendered dependent on the voltage set up atthe points 2) and d. For this purpose these points are interconnected through the potentiometer resistance R4. Since the point d has always a negative voltage with respect to earth a negative bias would be impressed through this potentiometer on the anode of the rectifierin case it did notreceive a positive bias through the point of connection of the resistances R2 and R3. Consequently a variable voltage is impressed on the potentiometer on either side. Of course, the voltage variations at the point (1 are small, so

that they cannot be applied with a highly decreased amplitude to the grids of the high frequency tubes. Consequently only a comparatively small part of the potentiometer may he between the point I) and the point e to which the grids of the high frequency tubes are connected.

Since the largest part of the potentiometer is consequently provided between 0'. and e, the influence of the voltage variations at the point at on the grids of the high frequency tubes will highly decrease. This voltage variation must be increased by increasing the resistance R5 to such an extent that at the point e the voltages re quired for regulating the slope of the tubes are obtained. It goes without saying that the various resistances represented in the arrangement need not be constructed in one piece, but that they may also be built up of several resistance elements if this be required by the construction of the complete amplifying arrangem nt.

When it is desired that the automatic volume control act only on the grid of one of the high frequency tubes an arrangement according to Figure 2 may be used in which a resistance is tapped at the point f of R4 which resistance is connected to the earth wire at the point it. If the grid of a second high frequency tube is connected to the point g then substantially voltage variations will be impressed thereon, which depend on the variations set up at the point (1.

Another case in which the grid bias of the high frequency tubes is made to be acted upon by two independent magnitudes is represented in Fig. Just as in the preceding arrangements the grid bias of the tubes is controlled in accordance with the strength of the incoming signals. This entails the drawback that in ranges between stations in which disturbances are received only, the amplification will be greatest. In order to avoid this the grid of the tubes during the tuning may be connected through a resistance R6 to a point of negative potential by closing the switch is thus reducing the amplification. Of course, the switch is may be replaced by a contact sliding over the resistance R6.

The auxiliary amplifier gain control device (1 acts with the tuner of the receiver to reduce undesirable effects caused by the AVC arrangement. If a receiver equipped with AVC is detuned so that no carrier wave is received, the sensitivity of the controlled amplifiers will be a maximum; this means that noise impulses are greatly amplified. Further, in such a case the stability of the controlled amplifier is small. Both of these undesirable effects, noise amplification and de creased stability, increase with increasing frequency to which the receiver is tuned. This follows from the fact that the amplification of the radio frequency amplifiers increases with increase frequency of tuning. It will now be clear that as the tuner is varied to increase the tuning frequency the device at is actuated to decrease the gain of the AVG-controlled tube. In this way the aforesaid undesired effects are greatly reduced.

While we have indicated and described several systems for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of our invention, as set forth in the appended claims.

What is claimed is:-

1. In a signal receiving system of the type including an electron discharge tube provided with means in its signal input circuit for tuning it over a desired signal frequency range, the gain of said tube, in the absence of signals at the high frequency end of said frequency range, being sufficiently high to cause undesirable noise amplification and instability, a signal rectifier for producing a variable direct current voltage whose magnitude depends on the received signal amplitude, and means for applying the voltage to a gain regulation electrode of said tube in a sense to decrease the gain thereof as the signal amplitude increases, said system being characterized by the further inclusion of auxiliary gain control means operatively associated with said tuning means for conjoint adjustment therewith, said auxiliary gain control means including a variable direct current voltage source connected to said regulation electrode in a sense such that the gain of said tube decreases, as said tuning means is adjusted towards the high frequency end of said range, to an extent sufiicient to reduce said undesirable effects in the absence of signals.

2. A method of operating a receiver of the type including a tunable signal amplifier and a signal rectifier which consists in automatically regulating the gain of the amplifier in response to variations in the space current flow of said rectifier to maintain the signal amplitude at the rectifier input substantially constant, tuning said amplifier over a desired signal frequency range, and decreasing the gain of the amplifier conjointly with said tuning and in opposition to the action of said automatic gain regulation, when the amplifier is tuned solely to the high frequency end of said range, to an extent sufficient to prevent undesirable noise amplification and amplifier instability in the absence of signals.

3. In a radio receiver of the type including a si nal amplifier tube provided with means for tuning its signal input circuit over an operating signal frequency range and a diode rectifier having signal input connections thereto, a source of direct current, a resistive path connected across said source, the diode electrodes being connected across a portion of said path in a sense such that the diode anode is positive with respect to the diode cathode, a second resistive path connected between the diode electrodes, the second path being in shunt with said first path portion, the amplifier cathode being maintained at the diode cathode potential, means for connecting the amplifier input grid to a point on the second path, and means for adjusting the resistive value of said second path whereby the effective bias of said amplifier grid is variable.

4. In a receiver as defined in claim 3, means for simultaneously operating said amplifier tuning means and said resistive adjusting means.

5. In a signal receiving system of the type including an electron discharge tube provided with means in its signal input circuit for tuning it over a desired signal frequency range, the gain of said tube, in the absence of signals at the high frequency end of said frequency range, being sufiiciently high to cause undesirable noise amplification and instability, a signal rectifier for producing a variable direct current voltage whose magnitude depends on the received signal amplitude, and means for applying the voltage to a gain regulation electrode of said tube in a sense to decrease the gain thereof as the signal amplitude increases, said system being characterized by the further inclusion of auxiliary gain control means operatively associated with said tuning means for conjoint adjustment therewith, said auxiliary gain control means being constructed and arranged to decrease the gain of said tube, as said tuning means is adjusted towards the high frequency end of said range, to an extent sufiicient to reduce said undesirable efiects in the absence of signals.

HERRE RINIA.

J OSEPHUS BOUMAN. 

